It has been proposed that the inactivation of glucocorticoids by the enzyme 11β-hydroxysteroid dehydrogenase (11β HSD) is an obligatory step in the kidney, permitting binding of aldosterone to the mineralocorticoid receptor, and in the placenta, protecting the fetus from high circulating levels of maternal glucocorticoids. Both low and high affinity isoforms of 11β HSD are known to exist, with evidence accumulating that the former species (11β HSD1) does not fulfill criteria that would allow it to perform these physiological functions. We have recently cloned a high affinity isoform of the enzyme (11β HSD2) from a human kidney library and have shown this species to possess all of the characteristics predicted from whole cell studies. In the present study we have raised a polyclonal antibody (HUH23) to a synthetic peptide deduced from the carboxy-terminus of the protein. The immunopurified antibody recognized a single band at 41,000 daltons on Western blots of mammalian cells transfected with an expression plasmid containing 11β HSD2, slightly smaller than the predicted 44,140 daltons protein. A single band of identical size was also seen in blots of human kidney and placenta, suggesting post-translational processing of the enzyme. Immunohistochemical studies on frozen sections of human kidney showed strong 11β HSD2 immunoreactivity in the cortical distal convoluted tubules and collecting ducts. Strong staining was also observed in medullary tubules, which had the appearance of collecting ducts and the thick ascending limb of Henle's loop. Staining of medium intensity was observed in vascular smooth muscle cells. Epithelial cells of glomeruli showed weak but detectable reactivity with HUH23. In the placenta, HUH23 antibody immunoreactivity was restricted to syncytial trophoblast cells in which strong staining was observed. These results suggest that the 11β HSD2 enzyme colocalizes with the mineralocorticoid receptor in the distal nephron where it allows aldosterone to occupy its physiological receptor. Furthermore, 11β HSD2 is also ideally situated in the placenta to protect the fetus from high circulating levels of maternal glucocorticoids.
|Number of pages||7|
|Journal||The Journal of Clinical Endocrinology and Metabolism|
|Publication status||Published - 1 Jan 1995|